Major-General Sir William Ponsonby KCB (13 October 1772 – 18 June 1815) was a British Army officer and politician who served in the Napoleonic Wars and was killed at the Battle of Waterloo.

[1] Together they had five children: Between 1796 and 1798, Ponsonby sat as a Member of Parliament (MP) in the Irish House of Commons for the Tories and represented Bandonbridge.

When Ponsonby's command, the 5th Dragoon Guards, arrived in the Peninsula in October 1811, it became part of John Le Marchant's heavy cavalry brigade.

[3] Upon Le Marchant's death in the battle, Ponsonby took over the brigade,[4] participating in the campaign that included the Siege of Burgos.

On 25 January 1814, Ponsonby took leave of his brigade and in the final battles in France, Lord Charles Manners exercised command.

The Scots Greys in particular, forgetting their supporting role and ignoring the "recall", charged on in disordered groups, some of whom reached the French guns on the other side of the valley.

[8] Following Ponsonby's death, command of the Union Brigade devolved upon Lieutenant-Colonel Arthur Clifton of the 1st Royal Dragoons.